The rapid proliferation of local area network (LANs) in the corporate environment and the increased demand for time-sensitive delivery of messages and data between users has spurred development of high-speed (gigabit) Ethernet LANs. The 100BASE-TX Ethernet LANs using category-5 (CAT-5) copper wire and the 1000BASE-T Ethernet LANs capable of one gigabit per second (1 Gbps) data rates over CAT-5 data grade wire require new techniques for the transfer of high-speed data symbols.
A 1000BASE-T Ethernet LAN driver requires an operational amplifier (opamp) capable of driving low impedance loads (i.e., 50 ohm transmission lines) with a large signal swing and high linearity. In order to reduce high frequency energy, the data signal must also be low-pass filtered to 90 MHz. In conventional operational amplifier applications, this means that the opamp used in the filter must have a unity gain frequency which is much higher than 90 MHz. In order to achieve such a high unity gain bandwidth, a conventional opamp operates using a large amount of current (i.e., high power consumption). The high unity gain frequency also makes it difficult to stablize the operational amplifier and it usually suffers from poor phase margins. The operational amplifier also undergoes a degradation in the unity gain bandwidth due to the presence of an input pole in the feedback path.
Therefore, there is a need in the art for an improved operational amplifier that consumes less current when driving a low impedance transmission line. In particular, there is a need in the art for an operational amplifier that does not require a unity gain bandwidth that is much larger than the low-pass filtered frequency band of the transmission line. More is particularly, there is a need in the art for an operational amplifier that eliminates the input pole in the feedback path.